ShowParameterPrompt property not working in SSRS ReportViewer API

Question

I'm trying to enable ShowParametersPrompt in the SSRS ReportViewer API - Microsoft.Reporting.WebForms API.

Help would be appreciated as it's not showing the parameters in my report. Only the toolbar is enabled.

                    rptViewer.ProcessingMode = rs.ProcessingMode.Local;
                    rptViewer.ShowParameterPrompts = true;
                    rptViewer.ShowToolBar = true;
                    rptViewer.LocalReport.ReportPath = physicalReportPath;